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RE: Wood Grading Stamp

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David,

First of all, to some degree, once you started cutting that "ton of wood
for a backyard project", the grading stamp on you lumber (as opposed to
timber) becomes worthless.  Grading of wood is a function of dimensions of
the member in question (i.e. span and cross-section dimensions if I recall
correctly...been a while since I read a grading book and the memory is not
what it was).  An example is that one difference between grades like No2
and Select Struct is the number and size of "permitted" knots in the
middle 1/3 of the span (i.e. where the bending stresses would be greatest
for flexural members).  Thus, if you bought a 20 ft 2x6 with a stamp for
stay Select Struct and then cut it into 2 10ft beams, then the grade stamp
that you have is potentially no longer valid (it might still be valid if
the size and number of knots along the whole length meet the requirements
for the middle 1/3 of the span for Select Struct).

This is one reason why timber used in the timber framing world is
generally not grade stamped...at least at the mill.  As timber frame
members will generally be cut significantly in a fabrication shop relative
to the original "sticks" shipped from the mill, any grading done at a mill
could likely be worthless for the final product.  The moment we start
cutting the timber, we could be changing the grade.

Another reason is that timber is generally not grade stamped is that is is
generally left exposed for aesethic (as in the "rustic" look that was
mentioned) and architectural reasons.  Now if you just paid a bunch of
money to have a timber framed home with a lot of exposed timbers for
aesethic reasons (i.e. want that "rustic" look), would you want a wonder,
black ink grade stamp staring back at you while sitting in your "rustic"
home in front of the fire?  Don't think so.  Thus, the general practice in
the timber frame industry is that timbers will not be physically stamped,
but if proof of grade is required to have the grader provide a letter
certifying it as such.  Obviously, it is not as "clean" from a verifiable
view (i.e. it is much easier to be confident of the grade when you can
look a stamp on the wood piece in question), and as such may not be as
desireable from the engineers perspective.  But, then how do you really
know that a steel W shape that you are looking at in the field is really
to ASTM A572 or A992 as oppposed to only A36...each steel member is
generally not stamped, but rather is covered by a mill cert.  Similiar for
concrete members...how do you know that the column you are looking at is
5000 psi concrete rather than 3000 psi concrete that was used for
footings?

HTH,

Scott
Adrian, MI


On Thu, 8 Sep 2005, David Maynard wrote:

> First, I agree with Jordan on this one.  I think the contractor is trying to take you for a ride and tell you what you designed.  Time to stand up for your specs and say, "Hey, this is what I called out.  Do it just like that.  Don't tell me!!!"  Or something along those lines in a more diplomatic but professional matter none the less.  This sounds like a contractor looking to save a buck by using some scrap he had in his yard.  But who really has 8" square timbers lying around???  I get off topic, sorry.  Nevertheless, he has to provide some sort of proof for this.
>
> Second, I didn't think timbers actually came without a stamp.  This leads me to my next thought, did the contractor have the stamp sanded off???  If so, why???  And don't give me this "rustic element" garbage, Mr. Contractor.  My guess is that his timbers he ordered possibly didn't meet your spec, so he eliminated the evidence, and is using this excuse to skirt the issue.  After buying a ton of wood for some backyard construction of my own, I found every stick to be stamped "SPF #2 or better" with an Fb value on it.  Then again, those were all 2x6's.  Not sure what you see when you get into bigger stuff like 8x8's.  Does Pressure Treated lumber come stamped as well???  I would imagine it does, but I don't do enough with timber to know for sure.
>
> Others may be able to shed a little more light on my issues.  Nevertheless, don't let the contractor get away with a garbage argument like this.  Bleh!!!!  Kinda sounds like, "We've done things like this all the time and have never had a problem before."
>
> Dave Maynard, PE
> Gillette, Wyoming
>   -----Original Message-----
>   From: Jordan Truesdell, PE [mailto:seaint1(--nospam--at)truesdellengineering.com]
>   Sent: Thursday, September 08, 2005 9:26 AM
>   To: seaint(--nospam--at)seaint.org
>   Subject: Re: Wood Grading Stamp
>
>
>   That argument is, excuse my language, bullsh!t. I wouldn't sign off on it unless the timbers were massively overdesigned and I knew that I could make the job work with absolutely lousy wood.
>
>   The best thing to do is to make him get the timbers graded and accept a letter of grading from a properly trained expert.  Let him know that if the grade is weaker, he'll have to pay for a re-analysis and may still need to get stronger timbers based on your new analysis and the timeber grade he has.
>
>   joraljim(--nospam--at)prtc.net wrote:
>     I designed a small wood dock structure supported on 8"x8" timber elements. In the contract documents, I specified that the each piece of lumber shall have a grade stamp of grading agency.
>
>     The contractor provides timber elements without any stamp, arguing that the timber are "rustic" elements.
>
>     Is that argument acceptable?
>
>     Jorge Jimenez, EIT
>
>
>
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